Dynamic optical response of solids following 1-fs-scale photoinjection

Photoinjection of charge carriers profoundly changes the properties of a solid. This manipulation enables ultrafast measurements, such as electric-field sampling^1,2, advanced recently to petahertz frequencies^3-7, and the real-time study of many-body physics^8-13. Nonlinear photoexcitation by a few-cycle laser pulse can be confined to its strongest half-cycle^14-16. Describing the associated subcycle optical response, vital for attosecond-scale optoelectronics, is elusive when studied with traditional pump-probe metrology as the dynamics distort any probing field on the timescale of the carrier, rather than that of the envelope. Here we apply field-resolved optical metrology to these dynamics and report the direct observation of the evolving optical properties of silicon and silica during the first few femtoseconds following a near-1-fs carrier injection. We observe that the Drude-Lorentz response forms within several femtoseconds-a time interval much shorter than the inverse plasma frequency. This is in contrast to previous measurements in the terahertz domain^8,9 and central to the quest to speed up electron-based signal processing.